In this description, medium-voltage cables refer to cables that are used in the voltage range of 12-36 kV, and high-voltage cables refer to cables that are used in the voltage range exceeding 36 kV.
When jointing a cable, the conductors from two cable ends are joined together with a jointing sleeve after the respective conductor has first been exposed from the surrounding insulation. The jointing sleeve brings the sleeve into contact with the conductor by means of mechanical deformation. The joint with the jointing sleeve must then be insulated. This insulation is usually carried out with a prefabricated tubular elastic body of rubber, hereinafter called jointing body. Known jointing bodies are usually formed with a substantially cylinder-shaped shell. The actual jointing body is provided with a continuous cylindrical hole, where the hole in the natural, non-stretched, state has an inner diameter that is somewhat smaller than the outer diameter of the insulation on the cable to be jointed. This is necessary for the elastic jointing body to embrace the insulation of the cable ends for the purpose of obtaining a closefitting joint.
When jointing is to be carried out, the work is initiated by placing the jointing body in a position over one of the cable ends, i.e. before the jointing sleeve has joined the conductors together. Moving a jointing body over a cable without first stretching the jointing body is difficult and allows the jointing body to be used only on a cable with a well-defined outer diameter that is adapted to the size of the jointing body. It is especially difficult for jointing bodies designed for medium- or high-voltage cables as those jointing bodies has a larger amount of elastic material that has to be stretched out. It is therefore common for the jointing body to be stretched onto the tube before the jointing body is brought into place. The jointing body is brought into place by first placing it over one of the cable ends, and after jointing the conductors the body is arranged over the joint.
It is known to stretch the jointing body onto a thin tube of, for example, a polymer at the factory making jointing bodies. The jointing body with the tube then has an inner diameter that is larger than both the outer diameter of the cable being jointed and a possible jointing sleeve in the joint. Therewith the jointing body may be easily fitted onto the cable according to the above description. A drawback of this arrangement is that the jointing body will be expanded for a long time and there is a risk that the rubber settles and possibly loses its re-sealing power, or that the storage time of the jointing body becomes limited.
A known way to avoid this is to stretch the jointing body onto a tube in connection with the jointing to be carried out. EP 0 707 749 B1 discloses a mounting tool for expanding a jointing body on a rigid tube before the jointing body is applied over the joint. The jointing body comprises a first end part and a second end part. The mounting tool comprises a rigid tube and an expansion cone insertable therein. When the expansion cone is fully inserted into the rigid tube, the expansion cone is arranged with is widest part at one end of the rigid tube. The expansion cone and rigid tube is inserted into the jointing body by firstly inserting the end with the cone into the first end portion of the jointing body, whereby the first end portion is expanded onto the rigid tube. The rigid tube has a larger inner diameter than the cable, and allows the expanded jointing body to be easily fitted over the cable after withdrawal of the expansion cone from the rigid tube. The expansion cone is provided with a handle extending through the rigid tube. The same procedure is used for the second end portion of the jointing body, which is expanded in the same way allowing the entire jointing body to be easily fitted over one of the cable ends. A drawback with this known tool is that it is difficult to remove the expansion cone through the rigid tube after the jointing body has been expanded on the rigid tube. Also, the edge of the rigid tube at the connection to the largest diameter of the expansion cone has to be very sharp to form an even, smooth transition towards the expansion cone. This sharp edge may damage the inside of the jointing body when the mounting tool is pushed into the jointing body.
There is therefore a need for an expansion device which overcomes the above drawbacks.
In the above description a jointing body has been described as an example of an elastic tubular body. Other examples of elastic tubular body for high-voltage or medium-voltage cables are a stress cone, a termination, a shielding or sealing sleeve or an adapter. Elastically expandable adapters are used to adapt a cable joint or a stress cone, with an inner diameter adapted to a certain cable diameter, to a cable with a smaller cable diameter. By using adapters, a cable joint or a stress cone may be used for a plurality of different cable diameters. A stress cone is used in a cable joint or a cable termination.